Probably you're experiencing problems because the latest version of the article is based on the newest release of JBoss Identity (called picketlink) which is to be released soon. If you like to use the 1.0.0.beta3 version, use version 4 of the article. You can find it here:
The changes with the latest version of the article (version 5) can be found here:
2) You probably mean the URL of the Assertion Consumer Service? You can use http://www.yourserver.com/<app-root>/AssertionConsumerService.seam. In fact any URL that is picked up by the Seam servlet will do.
3) In components.xml, you can configure whether the Seam authentication filter should validate that the assertion contains a valid signature (signed with the private key of the IDP). You do this with the signatureRequired parameter (which is true by default). If signatureRequired is true, the parameters keyStoreURL, keyStorePass and idpCertificateAlias are used to locate the certificate of the IDP.
Hope this will help you. Your questions and the problems you experience indicate that version management for JBoss Identity is still to be improved. :-)